Note: Descriptions are shown in the official language in which they were submitted.
~ 727 i3
WO 95/094S4 PCT/US94/10969
'~T~A~(~I FREQI~NCY MOBILE ANTh~l~A SYSTE;I~i
.
BAC~GRO~ND OF TR~ l~.v~ ON
The present invention relates to communication
antenn~s and to RF signal transmission through a dielectric
barrier. More particularly, it relates to a new and
improved glass mount mobile vehicle antenna system
employing very high Q, high dielectric constant, low loss
dielectric resonators, together with an elevated feed
antenna to couple RF energy through the glass via resonance
mode coupling of the resonators to minimize coupling losses
and to provide an improved omni-directional communication
antenna system having high radiation e~ficiency and low
pattern distortion.
Technological advances in personal communication
service~ and product~ have been asto~ ng. The develop-
ment of personal paging/heerer systems and mobile cellular
telephone systems are prominent examples o~ these develop-
ments. An ultimate tec~nological goal in this field
envisions individuals carrying small, in~Yr~sive hand-held
communicators and being reachable by voice or data with a
single phone number, no matter where they are. This new
system, generally referred to a~ a Personal Communications
Network (PCN)/Personal Communications System (PCS), is a
wire-less, ~go anywhere" communicator ~ystem which
eliminate~ the need for separate num~ers for the office,
home, pager, facsimile or car. Many national and interna-
tional bodies responsible for regulating communicationsnetworks and for working out international communication
st~nA~rds have generally set aside a portion of the ultra-
high frequency microwave radio spe~LL~ within the band
from about 1.5 GHz to about 2.4 GHz as the bandwidth range
dedicated for PCN/PCS communication systems. The present
invention is directed to mobile an~enn~a and especially
window mounted mobile vehicle antenn~C for use in any
CA 02172713 1998-08-14
communications system, but which are especially adapted for
use in the high frequency operating ranges intended for
PCN/PCS communications.
Glass mount mobile ant~nAC for use in cellular
mobile telephones, for example, are known which mount on
the window of the vehicle, thereby avoiding the need to
drill holes in or otherwise modify the vehicle body.
Window mounted ante~nAc include an outside module on the
outside of the window glass on which a generally vertical
radiating element is mounted and an inside module inside
the glass disposed in registration with the outside module
which contains an impedance-matching circuit and in some
instances, a ground plane, as necessary, for operation of
the antenna. Consumers have welcomed the through-glass
mounted ant~nn~C because it is no longer neC~cc~ry to drill
a hole through the vehicle which detracts from the
vehicle's value. However, the blocking effect of the
passenger compartment, coupled with through glass signal
losses occurring with most glass mount antennAs, provides
an antenna having a lower gain and a higher pattern
distortion than the roof-mounted antenna. Gain, for
example, is normally in the 1-3 dB range. Most cellular
telephone communications occur at operating frequencies of
about 800 MHz. Even at these lower frequencies, improved
coupling efficiency and lower distortion is desired.
Efforts at improving the performance of prior art
glass mount mobile ante~nAC have employed capacitive
couplings through the vehicle glass and low-Q circuits
involving LC impedance matching networks. For example, in
U.S. 4,089,817 to Kirken~Ahl, a capacitively coupled
antenna system is described. The capacitive coupling
consists of electrical patches on both sides of the
automobile glass, such as a windshield or window, which
forms a capacitor to couple the RF energy. In U.S.
4,839,660 to Hadzoglou, an improved structure including a
CA 02172713 1998-08-14
moderate coupling impedance wherein the bottom radiation
element is close to a complete half-wave dipole is
described. A full-dipole radiation element cannot be used
because of the high transmission impe~Ance sensitivity at
one half wavelengths. Other illustrative examples of glass
mount antennas employing different circuits to provide
impedance matching networks for capacitive couplings
include U.S. 4,992,800 to Parfitt; U.S. 4,857,939 to
Shimazaki; and U.S. 4,785,305 to Shyu.
Each of these previous efforts to provide
capacitive coupling by positioning electrical patches on
both sides of the vehicle glass presents a number of
att~n~nt disadvantages. The electrically conductive
patches generally may not be made large enough in
comparison with the operating wavelength to keep it from
being the primary radiating element. Accordingly, only
high impedance couplings on the order of several hundred
Ohms may only be provided which leads to high losses due to
leakage of the electrical field at higher frequencies. At
higher frequency bands like the proposed PCN/PCS band, even
a small conductive patch is no longer effective to act as
a lump capacitor element considering the thickness of the
vehicle glass. A capacitance PI circuit bypasses the
signal and makes it more difficult to match the high
impedance of the antenna to a 50 Ohm system. In U.S.
4,764,773 to Larsen, an improved coupling structure is
proposed, including two patches to reduce the coupling
imp~nc~. The Larsen antenna, however, still suffers from
having the capacitor coupling limitation of requiring small
patch sizes. At higher operating frequencies, this problem
still exists or exacerbated.
For mobile communications, it is critical to
provide an antenna system having low pattern distortion.
A whip collinear antenna does not always have a uniform
current distribution. Frequently, a lower section has the
CA 02172713 1998-08-14
strongest radiation. In a real-life automobile or other
vehicle situation, the lower section of these antennas is
actually blocked by the roof of the vehicle, causing sever
pattern distortion and deep null. This situation is made
worse at the higher proposed frequencies for PCN/PCS
because the length of the radiators are only half that of
the cellular band radiator, is to the doubling of the
operating frequencies. A collinear, having a high feeding
point, is normally provided by applying a de-coupling
sleeve or by means of slot technology. These antennas
normally have a 50-75 Ohm imp~Ance which makes it
difficult to adapt these antennAs to the capacitively
coupled prior art structures. As a result, outside
impedance matching networks must be used to achieve a 50-50
Ohm transmission and even higher losses are expected at the
higher PCN/PCS frequency bands when these at conventional
LC circuits are employed.
Another major shortcoming of prior art capaci-
tively coupled antenna systems is that these kinds of
systems suffer strong spurious emission to the passenger
compartment simply because the whip collinear array needs
a ground plane. Prior art methods used to isolate the
feeding line from environmental radiation have relied on
the couplers themselves to act as an impedance matching
network. For example, in the above-mentioned Hadzoglou and
Kirken~Ahl patents, the coupling patches are part of the
antenna's impedance matching network. In U.S. Reissue
Patent 33,743 to Blaese, another capacitively coupled
antenna system is described which attempts to couple the
coaxial cable through the glass. At high frequency
PCN/PCS bands the proposed 1/4 wave antenna would be only
about 1.7 inches long, which would lie completely below the
roofline of the vehicle causing severe pattern distortion
and deep null. In U.S. 4,939,484 to Harada, a coupler
including helix cavities is used to couple the signal
W095/09454 21 7 2 7 ~ 3 PCT~S94110969
through the glass. Unfortunately, the aperture is fixed to
satisfy the 1/3 object frequency, as described in the
Harada patent. For an 800 MHz cellular application, the
helix should be designed for a 200 MHz freque~cy which has
a Q factor of over 1,000 and enough coupling aperture.
However, at a 1.8 GHz frequency band, the helix must be
designed for 600 MHz. A 600 MHz helix cavity will have a
small aperture of only about half that of the cellular
band. A significant drop of unloaded Q is unavoidable, due
to the thin helix and the coupling co-efficient is n~t
sufficient to keep a 10% band Width. Other drawbacks of
the helix cavity approach described in the Harada patent
are that in the proposed anten~A~, it is difficult to tune
the frequency of the antenna system and it is difficult to
manufacture the an~Pnn~c because of its complicated
structure.
Generally, the performance of the prior art
antenna system~ degrades considerably as freguencies
approach the 1.5 GHz to 2.4 GHz range ~G~o~ed for PCN/PCS
co~munications. The prior art ant~n~Q and systems are
relatively low frequency systems, when compared to
microwave frequencies and they all employ low Q, lumped LC
elements, or semi-lumped elements provided by placing the
LC element~ in metal enclosures. At the higher PCN/PCS
frequencies, the losses of LC circuits will increase
con~iderably due to the low, unloaded Q nature of the prior
art systems and components. The PCN/PCS communication
systems must operate at low power levels of about 1 Watt
and provide a very wide range of cove~age at very high
freguencies. The prior art antenna systems are ~nA~ o~
ate for satisfying these requirements because of their low
frequency approaches.
It is known in the filter arts that certain
dielectric resonators may be used to ~uild high-quality,
narrow-banded filters, typically less than 2%. In filter
CA 02172713 1998-08-14
applications, the dielectric resonators are normally placed
in a continuously conductive enclosure to minimize any
losses which may arise due to spurious modes or leakage.
Illustrative dielectric resonators are described in U.S.
2,890,422 to Schlicke. The dielectric resonators have very
good long-term stability so that component aging effects
are negligible. The high density nature of the resonators
reduces the undesirable effects of moisture to a minimum.
Even at high frequency bands around 1.8 GHz, dielectric
resonators may still maintain an unloaded Q factor of
greater than about 3,000. In contradistinction, the helix
cavities with a 600 MHz based frequency described in the
Harada patent, cannot achieve such a high Q factor. Th~
hollow-cavity helix systems described in the patent are
more sensitive to the environment than dielectric
resonators and special sealing is reburied to keep the Q
from dropping further. Furthermore, it is impossible to
keep sufficient coupling coefficient for a *small helix
aperture through a vehicle glass having a thickness from
about 4 to about 6 mm, plus the thickness added by any
adhesive mounting pads. The dielectric couplers solve the
aperture problem of the Harada patent because the
dielectric constant can be selected. For example, at 1.8
GHz, a dielectric resonator with a constant of 80 available
commercially from Trans-Tech, Inc. under the trade
designation 8600 Series has a dimension of D=24 mm, and
h=7.6 mm. At 2.4 GHz, a dielectric resonator with constant
of 38 also commercially available from Trans-Tech, Inc.
under the designation Series 8800 may be used which has the
dimensions D=24 mm and h=9.6 mm, which still provides a
large enough aperture to maintain the coupling coefficient
at a desirable level. On the other hand, an 800 MHz base
frequency helix may have only a 10 mm aperture.
Accordingly, to overcome the shortcomings and
disadvantages of the prior art systems and devices, it is
CA 02172713 1998-08-14
an object of the present invention to provide a new and
improved glass mount antenna system.
It is another object of the present invention to
provide a glass-mount antenna system adapted to operate at
s upper UHF and higher microwave frequencies exhibiting
greater coupling efficiency and less pattern distortion
than has heretofore been achieved.
It is a further object of the present invention
to provide a coupling scheme including a new and improved
tuneable wide band coupling structure which provides
flexible impedance matching to permit the feeding point of
the antenna to be raised easily.
It is still another object of the invention t~
provide an antenna system having improved emission
performance by employing twin enclosed cavities containing
moisture-insensitive, high Q dielectric resonators and by
implementing a feeding line isolating choke at the antenna
end.
It is still a further object of the present
invention to provide a glass-mount antenna system employing
a resonance mode coupling, such as TE011 and TE111 modes,
instead of electrical capacitance or inductance couplings.
It is still another object of the present
invention to provide a high performance omni-directional
PCN/PCS communication antenna system capable of coupling
high frequency RF energy through a dielectric wall without
the need for a continuously conductive enclosure and
without significant losses.
SUMMARY OF THE lNv~l~loN
In accordance with these and other objects, the
present invention provides a new and improved antenna
apparatus for mounting on the window of the vehicle which
is adapted for operation in conjunction with a utilization
device, such as a communication device, located within the
vehicle. More particularly, the antenna apparatus
W095/09454 21 7 2 7 1 3 PCT~S94/10969
comprises an exterior module and an interior module. The
exterior module includes a first electrically conductive
shroud member defining a first shielded cavity. The module
additionally includes an elongated radiating element. A
first low-loss, high Q dielectric resonator element adapted
for resonant mode coupling is disposed in the first
shielded cavity. Means are provided for electrically
coupling the radiating element to the first dielectric
resonator. Furthermore, means are provided for mounting
the exterior module to an outside surface of the vehicle
window so that the radiating element is disposed in an
elevated feeding position.
The antenna apparatus additionally comprises an
interior module which includes a second electrically
conductive shroud member defining a second shielded cavity.
A second low loss, high Q dielectric resonator element is
disposed in the second shielded cavity and is adapted for
resonant mode coupling with said first dielectric resona-
tor. A coaxial feed line including an inner conductor and
an outer conductive shield is provided for electrically
coupling the interior module to said utilization device.
The inner conductor of the feed line is electrically
coupled to the second dielectric resonator. The outer
conductive shield is electrically coupled to the second
conductive shroud mem~er. Means are provided for mounting
the interior module to the inside surface of the vehicle
window in general alignment with the exterior module so
that the first dielectric resonator and the second
dielectric resonator are disposed substantially in
registration.
In accordance with the preferred embodiment of
the invention, both the exterior module and the interior
module are additionally provided with an electrically
nonconductive dielectric outer housing adapted to sur-
roundingly engage and protect the first and second
CA 02172713 1998-08-14
electrically conductive shroud members. The preferred
radiating elements will comprise semi-rigid coax-sleeve
dipole type radiating elements. Semi-rigid coax-sleeve
dipole antennas having at least one RF choke end portion
are especially preferred. The dielectric resonators for
use in the antenna apparatus for this invention may
comprise dielectric resonators having a dielectric constant
of at least about 80 and a Q factor of at least about 3000.
Especially preferred dielectric resonators are cylindrical
ceramic materials selected from Barium-Titanium-a Lantha-
nide Series element- (and optionally lead) oxide ceramics,
such as, Ba-TI-Pb-Nd oxide ceramic and BA-Pb-Ti oxide
ceramic materials. Ceramics of this type are commercially
available from sources such as Trans-Tech, Inc. and Murata
Erie North America Company. Additionally, for ultra-high
frequency uses the ceramic may have a lower dielectric
constant of about 38 and a Q factor of at least about
30,000. In accordance with the preferred embodiment, the
inner or core conductor of the coax radiating element is
electrically coupled to the first dielectric resonator and
the outer radiator shield is electrically coupled to the
first shroud member. In accordance with the preferred
embodiment, the cylindrical ceramic dielectric resonators
will have an aspect ratio, i.e. a length to diameter ratio
(L/D) of less than about 0.4 to provide a satisfactory
coupling coefficient. In especially preferred embodiments,
large bandwidths are provided by employing metallic strip
exciters disposed adjacent the ceramic resonators and
between the resonators and the adjacent shroud walls.
In accordance with this invention, resonance mode
coupling, such as TE011 and TElll modes, instead of
electrical capacitance or inductance coupling, provides a
superior through glass antenna system for use at most
frequencies and especially at-high frequencies. More
particularly, the vehicle glass is a dielectrical material
WO 95/094~4 2 1 7 ~ 7 1 3 PCTIUS94/10969
-- 10 --
which introduces considerable dielectric loss at high
frequencies for electrical fields, but very low losses for
concentrated TE011 and TElll magnetic fields. TE011 and
TE111 modes have very low loss and the E,H field distribu-
tions make them very suitable for the glass couplerapplications. In accordance with this invention and
utilizing this coupling method, high performance antenna
systems for providing omni-directional communication with
high radiation efficiency and low-pattern distortion are
provided, especially at PCN/PCS frequencies of above about
1.5 GHz and preferably between about 1.5 GHz and 2.4 GHz.
Further objects and advantagea of the invention
will become apparent from the following Detailed Descrip-
tion of the Preferred Embodiment taken in con~unction with
the ~rawings, in which:
BRI~F DF~CRIPTION OF TH~ DRAW~GS
FIG. 1 is a pe~e~Live view of the new and
improved resonant mode through glasa antenna apparatus in
accordance with the preferred embodiment of the invention
shown in use in a mounted position on an automobile
w~ c~ield;
FIG. 2 ia an elevated croas-sQctional view of the
new and improved antenna apparatua o~ the invention shown
in FIG. 1;
25FIG. 3 is an exploded pe~e~ive view of the
antenna apparatus in accordance with the preferred
embodiment;
FIG. 4 is a perspective view with portions cut
away to reveal the structure of the exterior module and the
interior module of the new and im~o~l antenna apparatua
of the ~r~ent invention shown in their ~e~e_~ive
assembled form;
FIG. 5 i8 a simplified electrical schematic
diagram of the new and improved antenna of this invention;
35FIG. 6 is an elevated cross-sectional view of an
WO 95/09454 2 1 ~ 2 7 1 3 PCT/US94/10969
alternate antenna system in accordance with the present
invention shown in use mounted to an automobile windshield;
FIG. 7 is an elevated side-view partly in section
- showing another alternate embodiment of the new and
improved antenna system of this invention; and
FIG. 8 is a graphical plot illustrating the
insertion loss and corresponding VSWR plots of a TEOll
symmetrical mode glass coupler antenna apparatus in
accordance with the preferred embodiments shown at
increasing frequency values from 1.7 GHz to 1.9 GHz .
wos5/09454 ~ 17 2 7 13 pcT~ss4llo96s
DETAI~D DB8CRIP~ION OF T~E PR~FERRE~ ~M~ODIM~NT8
Referring now to Figs. 1-4, a preferred embodi-
ment of the new and improved antenna apparatus in accor-
dance with this invention, generally referred to by
reference numeral 10 is shown. As ~hown in the figures,
the antenna apparatus 10 includes an exterior module
assembly 14 and an interior module assembly 16 mounted on
a vehicle window 12. The vehicle window 12 may comprise
any dielectric window member within the vehicle and
preferably will comprise a front or rear wind screen with
the antenna apparatus 10 mounted adjacent an upper roof
portion thereof.
Exterior module 14 includes an outer dielectric
housing member 18 having a generally hollow cylindrical
configuration with a closed end 20 and an Gy~O~~d open end
22. A tubular angled radiator mounting sleeve 24 pro~ects
outwardly at an angle from the dielectric hou~ing 18. The
angle of the mounting sleeve 24 i8 preferably selected 80
that in its installed condition, the radiating element 26
is disposed in an elevated feed position, preferably above
the vehicle roof.
As depicted in the preferred embodimentQ shown in
Figs. 1-4, a margin portion of the housing ~Lounding open
end 22 is provided with a lip 28 having a latch-receiving
recess 30 defined therein. The dielectric housing 18 may
comprise any relatively ..G~ onducting dielectric thermo-
plastic polymer. Preferably, the dielectrical hou~ing
comprises a ~haped or molded polycarbonate member.
In accordance with the preferred embodiments
depicted in Figs. 1-4, the radiating element 26~ will
comprise a semi-rigid coax sleeve dipole radiator including
an outer shield member 32 and an inner con~ tor 34. The
coax dipole radiator element 26 include~ an outwardly
projecting free end 36 provided with an RF choke 38. The
radiator 26 is preferably protectively covered in a
WO 95109454 l~ 1 7 2 7 1 3 PCT/US94/10969
-- 13 --
dielectric sleeve 40 which may be made of any suitable
thermoplastic polymer material, such as a thermoplastic
polyester or a polyolefin. The protective sleeve 40 in
accordance with the preferred embodiment is adapted for a
slidable press-fit engagement onto the mounting sleeve 24
of dielectrical housing 18. The outer shield 32 and inner
conductor 34 from radiator element 26 extend through an
interior portion of mounting sleeve 24 to make an appropri-
ate electrical coupling to other members of the exterior
module 14, to be more particularly described hereinafter.
In accordance with this invention, the exterior
module 14 additionally comprise~ a first electrically
conductive shroud member 42 having a hollow open-ended
cylindrical configuration inclu~ing a closed end wall 44
and an opposed open end 46. A plurality of cap mounting
notches or ~Looves 48 are provided in the sidewall of
shroud member 42 adjacent open end 46. An aperture or feed
hole 50 extends through a sidewall portion of shroud member
42 to permit the in~ Ated inner çon~uctor 34 from the
radiator element 26 to pasfi therethrough. The outer shield
conductor 32 o~ radiator element 26 i8 electrically coupled
to the shroud member 42. Shroud member 42 define~ a
shielded recess or cavity 52 within the exterior module 14.
Shroud member 42 should be configured to be closely
tQlescopically received through the open end 22 of the
dieloctrical housing 18. Shroud member 42 may be made from
any suitable electrically ro~uctive material and, in
accordance with the preferred embodiment depicted herein,
the shroud member 42 i~ made of a bra~s alloy.
Exterior module 14 further includes a dielectric
planar substrate 54 such a~ a printed circuit substrate
having a cylindrical projectinq mounting pin 56 ext~n~i~g
from outwardly from one ma~or surfaco 60 thereo~. In
accordance with the preferred embodiment, a loop-ehAped
rond-~ctive region 58 forming an exciter ~trip is provided
CA 02172713 1998-08-14
on major surface 60 of planar substrate 54. The dielectric
substrate 54 may comprises any suitable dielectrical
material although low loss materials such as ULTEM~
polyetherimide or other electrical grade thermoplastic
polymer, such as polystyrene, may be used. The conductive
exciter strip 58 may be in a looped configuration or a
straight strip configuration and may be plated onto the
planar substrate 54 or may comprise a separate metallic
member affixed to major surface 60 of the substrate 54 by
any suitable means such as, for example, by means of an
adhesive. The planar substrate 54 in accordance with the
preferred embodiment has a think cylindrical or disc shaped
configuration having a diametrical dimension selected to be--
closely telescopically received in the first shroud member
42 so that a second major surface 62 is disposed in
abutting face-to-face relation with the closed end 44 of
the shroud member 42.
The thickness dimension of the planar substrate
54 is selected so that the exciter strip 58 is spaced a
predetermined distance from the closed end 44 of the shroud
member to define a desired impedance therebetween. The
inner conductor 34 from the coax radiating element 26 is
electrically coupled to the conductive metal strip 58 on
the first major surface 6q of the planar substrate 54. Any
suitable electrical coupling means may be used to achieve
this result.
In accordance with the preferred embodiment, the
exterior module 14 additionally comprises a dielectric
resonator element 66 having a generally cylindrical
configuration provided with a central core aperture 68
exten~ing therethrough. Resonator element 66 is
preferably a low-loss, high dielectric constant, high Q
dielectric resonator made from ceramic materials having a
dielectric constant of at least from about 75 to 100 and
preferably at least about 80. Resonator element 66 may
be slidably received on mounting pin 56 of the planar
WO 9~/09454 217 2 7 1 3 PCT/US94/10969
-- 15 --
substrate 54 so that a major end wall surface 70 thereof is
disposed adjacent to the conductive region 58 comprising
the exciter strip defined on major surface 60 of planar
substrate 54. Optionally, but preferably, a small amount
of a suitable adhesive material may be disposed about the
mounting pin 56 and core aperture 68 to maintain end
surface 70 of resonator 66 in adjacent spaced relation to
the exciter strip 58.
In accordance with the preferred embo~iment
depicted in Figs. 1-4, exterior module 14 additionally
comprises a thermoplastic cap mem~er 72 having a thin disk-
like cylindrical configuration. Cap member 72 includes a
raised forwardly projecting lip 74 defining an adhe~ive-
receiving recess region 75 on an outwardly facinq ma~or
surface 77 thereof. Cap member 72 additionally includea a
plurality of rearwardly projecting ~ e.l latch arms 76
each provided with free end portion 78 equipped with
cooperating lockin~ latches 80 intended to releasably
engage the ~ oove recess 30 provided in lip 28 on dielec-
tric housing 18 to secure the exterior module 14 in a fullyassembled condition. Cap member 72 includes a plurality of
curving slot~ 82 defined radially inwardly from an edge
portion thereof which are adapted to receive the raised
edge portions defined between ad~acent notches 48 in first
shroud member 42. In the fully assembled condition as
shown in Fig~. 2 and 4, the recQnA ma~or surface 84 of
resonator 66 is positioned for flush mounting in face-to-
face contact against the outside surface of vehicle window
12.
In accordance with the preferred embodiment
depicted in Figs. 1-4, a means for mounting the exterior
module 14 to the vehicle window 12 preferably comprises an
adhesive pad material 86 having adhe~ive honAtng capabili-
ties dis~oEo~A. on opposed surfaces thereof. A preferred
adhesive pad 86 comprises an acrylic foam adhesive
*rB
CA 02l727l3 l998-08-l4
- 16 -
available from 3M Company.
In accordance with this invention, the new and
improved antenna apparatus 10 additionally comprises an
interior module 16 composed of component elements very
similar to those comprising the exterior module 14. More
particularly, and as best shown in Figs. 1-4, the interior
module 16 includes a second dielectrical housing 90 adapted
to receive a second electrically conductive shroud member
92 to define a shielded cavity 94 within the interior
module 16. A planar printed circuit substrate 96 provided
with an electrically conductive region 98 thereon is
provided which also includes a positioning pin 99 ex~en~ing
therefrom. A second dielectrical resonator 100 is provided- -
within the shielded cavity 94 of the interior module 16 to
provide resonance mode coupling in TE011 mode with the
dielectric resonator 66 of the exterior module 14.
Interior module 16 additionally includes a thermoplastic
polymer cap member 102 provided with the releasable
cooperative locking features to maintain the interior
module 16 in fully assembled condition. An 0-ring shaped
adhesive pad 104 is also provided on an outer facing
surface of the cap member to securely mount the interior
module 16 against the inner surface of the vehicle window
12. The interior module 16 iS adapted for electrical
2 5 coupling to a coaxial feeder cable 106 including an inner
insulated conductor 108 and an outer conductive shield 110.
A crimp ferrule-type connector 112 extends outwardly from
a sidewall of second shroud member 92 and through a groove
or recess 114 provided in dielectrical housing 90. The
conductive outer shield 110 of the coaxial feed cable 106
is electrically connected or coupled with the second shroud
member 92 and the inner conductor 108 is electrically
coupled to the conductive region 98 provided on planar
substrate 96. The remote end of the coaxial feeder line
106 iS in turn electrically coupled to the utilization
woss/094s4 ~ 17 2 713 PCT~S94/10969
- 17 -
device, such as a communication system, provided within the
vehicle.
Referring now to Fig. 5, a schematic simplified
diagram of the antenna system provided by the present
invention is shown. The antenna system 10 of this
invention relie upon more efficient RF coupling through
resonance mode coupling of the two matched dielectric
resonators such 66 and 100 to provide a high performance
omni-directional communication antenna.
In accordance with thi~ invention, the exterior
module 14 and interior module 16 are mounted on opposed
surfaces of vehicle window 12 in general alignment with
each other so that the dielectrical resonators 66 and 100
are disposed substantially in registration with each other.
The new and imy~o~ed microwave dielectric
resonators 66 and 100 used in the antenna apparatus 10 of
this invention have very low 1088 and high Q values in
comparison with the LC lumped circuits and distributed
transmission line systems of the prior art. In glass-
coupled antenna contexts, it is an important feature to
minimize the surface current on the sidewall of the metal
closures defined by first and ~econ~ shroud members 42 and
92, respectively. This is important because there is no
overall common enclosure in a glasa mount, through window
antenna situation. Accordingly, the dielectric constant of
the re-onAtors must be sufficiently high and the electro-
magnetic field distribution must be a~ iately consid-
ered in selecting the a~y~ 6~ iate rQ~o~A~cq mode.
In accordance with this invention, it i~ an
important structural aspect to attempt wherever possible to
avoid cutting surface ~,e..L. For this reason, high
dielectric constants for the dielectric re~onators 66 and
100 are required and ceramic ~ o~tor~ are especially
preferred. For this specification application, Barium and
Titanium based oxide ceramics including at least one
CA 02l727l3 l998-08-l4
-- 18 --
Lanthanide Series component and optionally a lead component
such as BA-Pb-Nd-Ti Oxide ceramic or BA-PB-TI Oxide ceramic
materials are preferred because of their high dielectric
constant values of 80 to 90. They also have high Q factors
and the unloaded Q versus frequency for these materials can
be approximately expressed as being from about 4500 to
about 9000/f(GHz). For higher frequencies of operation,
e.g., at or about 2.4 GHz, a Zr-Sn-Ti ceramic material may
be used which has a lower dielectrical constant on the
order of between about 20 to about 45 and preferably of
about 38 but a Q factor having a much higher value of
40,000 per/f (GHz). Traditionally, aspect ratios (L/D
ratios) for the dielectric resonators of L/D = 0.4 wer~
frequently used to insure that the nearest spurious mode
was avoided. In the design context for the antenna
apparatus of this invention, the glass wall effect should
be considered in designing to suppress spurious modes and
when using dielectrical resonator materials having a
dielectrical constant of 80, an L/D ratio of less than 0.4
is generally suitable for almost all kinds of passenger
vehicle glass.
In accordance with the preferred emhoAiments, the
exciter strips 58 and 98 are employed in combination with
the dielectric resonators to provide a wider bandwidth
coupling. Preferably, the exciter strips 58 and 98 are
selected to have an electrical length of less than about
0.25 waveguide wavelength and especially preferably will
have an electrical length of about 0.22 waveguide wave-
length. The impedance formed between the exciter strip 58
or 98 and the shroud end wall, such as 44 of the shroud
member 42, may be selected to be from about 50 to 100 Ohms
as required for any various antenna type.
Referring now to Fig. 6, an alternate antenna
apparatus 128 is shown. Antenna apparatus 128 includes a
radiator or antenna member 130 selected from any kind of
sleeve dipole or elongated collinear array type having at
CA 02l727l3 l998-08-l4
-- 19 --
least one RF choke 131 disposed at an end portion thereof
to isolate the feeding line emissions and to lift the
feeding point above roof level on the vehicle. A soft,
thin cable assembly 142 having an outside conductor
connected to a conductive shroud and having an
innerconductor soldered to the exciter strip comprises the
outside feed line. The end of the cable is connected to
the antenna member 130. Housings 120 and 141 have
essentially the same structure. Dielectric resonator
exciter assemblies are constructed in the shielded cavity
formed by the cylindrical conductive shroud housings 121
and 145 width dielectric resonator members 122 and 144
mounted inside by a support 143 and a coupler body 120;
respectively. The strip exciters 124 and 146 on the
sidewalls of the resonators 122 and 144 are metal strip
lines made by conventional printed circuit printing
tec~niques or are metal strips attached to the resonator
members 122 and 144. A cable 150 is the feeding line
connected to the PCN/PCS transceiver. A tuning plate 123
in accordance with this embodiment, may be provided to trim
the frequency of the overall apparatus 128. Alternatively,
the distance between the resonators may be changed because
the resonator pairs have a smooth tuning chart when
spurious modes are successfully suppressed. A tunable
antenna system of the type depicted in the antenna
apparatus 128 may be more useful when the thicknesses of
the glass window structures vary a great deal. Generally,
however, a tuning plate moveable toward and away from the
exciter strip 124 by rotation of a threaded screw member is
optional and not generally nececcAry.
In accordance with this invention, the dielectric
resonators may have a generally square configuration and be
adapted for TE111 mode coupling. TE111 couplers may also
be employed wherein the exciter strip is disposed on a side
edge surface of the resonating element. By way of
illustration only and not limitation, the square ceramic
CA 02172713 1998-08-14
- 20 -
dielectric resonators may have dimensions of about 23mm x
23mm x 7.lmm to provide resonators having a dielectrical
constant of about 80 and useful at 1.8 GHz band.
Referring now to Fig. 7, the above described
techniques are not limited to 50 to 50 Ohm couplings. By
modifying the width of the strip exciter members, the
antenna apparatus and coupling assembly may also work with
regular whip collinear array radiators having a lower
section length of nearly 1/2 wavelength of 5/8 wavelength.
In the prior art, collinear arrays with a 5/8 wavelength
lower section could not directly be used because the
capacitively coupled design required that the load had to
be inductive. As depicted in Fig. 7, an economical
arrangement for a typical 3 dB collinear whip is shown.
The collinear ship antenna is formed by elements 235
through 238 where 237 can either be 1/2 or 5/8 of
wavelength in length. The element 238 is a swivel foot
connected to the microstrip line member 272 which forms a
1/4 wavelength loop exciter strip on substrate 270 which is
adjacent to resonator element 244. Element 271 is the
ground plane on the other side of the microstrip line. The
imp~nc~ of the microstrip line can be from 50 to 75 Ohms
and then tapered to the required antenna base impedance.
The internal module coupling box 220 may generally be the
same as those described above.
Referring now to Fig. 8, a typical coupler used
for PCN band in accordance with the present invention
adapted for operating at frequencies ranging from about 1.7
GHz to 1.9 GHz shows that for the new and improved antenna
apparatus 10 of this invention less than a 1 dB loss
through a 6mm thick win~chield glass occurred over a
bandwidth of 11% at 1.8 GHz. The curve shown in Fig. 8
indicate that the spurious response is kept away from the
useful bandwidth. If a smaller bandwidth is preferred, the
insertion losses can be made even smaller due to the high
WO 95/09454 PCT/US94/10969
~172713
- 21 -
Q nature of the dielectric resonators.
Although the present invention has been described
with reference to certain preferred embodiments, modifica-
tions and changes may be made therein by those skilled in
thi~ art without departing from the scope and spirit of the
present invention a~ defined by the appended claims.
